Various arrangements have been provided in hydraulic clutch/brake pistons to overcome the slippage or momentary torque spikes (harsh engagement) between the disks located therein when an input torque is being transmitted therethrough or a braking or stopping effort is applied to the output thereof. It is recognized that the various arrangements could be hydraulic clutch arrangements or hydraulic brake arrangements. Slippage occurs when the disks are not fully in contact and torque is being delivered therethrough. Since the disks are not fully in contact, torque cannot be delivered therethrough. This is true because the disks slip one relative to the other. On the other hand, harsh engagement occurs when the disks are moved into forced contact prior to the torque being delivered therethrough. Since the disks are in full, forced contact, initiation of torque therethrough results in a jerk or sudden output being transmitted to the output. Additionally, it is desirable to detect or know when the end-of-fill occurs so that the input torque may be applied at the proper time. End-of-fill is the point at which all entrained air spaces between the respective disks and actuator piston are removed and the respective disks and actuator piston are in close, intimate contact. At this point, the hydraulic clutch/brake mechanism is in condition to begin transmitting torque therethrough. In some known systems, it has been necessary to calculate the needed flow and then precisely control the open of the control valve for a predetermined length of time in order to move the actuator piston to a position that is calculated to be the position of end-of-fill. Since this is a calculated procedure, there are many variables that affect its accuracy and consequently, its ability to reduce slippage and/or jerk at the point that torque is transmitted therethrough is minimized. One such arrangement to overcome harsh engagements is illustrated in U.S. Pat. No. 3,650,364 issued Mar. 21, 1972 to James Morrison Laing. This patent teaches the use of two separate actuator pistons for engagement. Pressurized fluid is applied to an area of one of the pistons to urge the disks into initial engagement with each other, then the pressurized fluid is directed through an orifice to simultaneously act on an area of the second piston to fully apply the clutch. Even though this arrangement does help to offset harsh engagements, it does not provide any cushioning or damping of the engagement of the disks nor does it provide any indication as to when the end-of-fill has been reached.
The subject invention is directed to overcoming one or more of the problems as set forth above.